Just follow the instructions in the advanced operation section of your manual.
Select SKIP in the SIZE function.
Make sure there is NO noise in the room. No noise period. The microphone is very sensitive.
I make sure there is no-one home, no ac/heat on, no fans on, no cars passing, and I even wait for the refrigerator to quit running.
I also step as far away from the action as I can, without leaving the room.
If you are in the line of any speaker, leaving the room during each operation may be a good idea.